Figured I’d comment here for those that still use it or may want to.

The website updated the code and it broke the module. I created a new pull request to fix it. Not sure this will get merged into main, but given it’s a static module with no updates in 6 years, it’s pretty safe to just manually replace the code in your local module.

https://github.com/rahultadak/MMM-CalvinAndHobbes/pull/3/files

Otherwise, I have forked it here. Not planning on updating it unless it breaks again and even then it will be as time allows.
https://github.com/B3DTech/MMM-CalvinAndHobbes